From Danish patent application No. 2001 00281 a roller membrane valve is known for maintaining constant liquid flow in a heating or cooling system. That valve comprises an electric regulator unit which is adapted to the valve.
By that known valve it is not possible to set a maximal flow within which the valve subsequently modulates or regulates.
From Danish patent disclosure DK 176350 B2 a valve is known wherein a maximal flow can be set by means of two concentrically journalled valve bodies.
It is a drawback of that system: that each of the valve bodies is expensive and complex, and that it is consequently not easy or inexpensive to replace those concentrically journalled valve parts.